Compressed air is widely used throughout industry as a safe and reliable source of energy. However, the quality of the compressed air delivered directly from the compressor is unsuitable for most uses without treatment to improve its purity. Treating compressed air generally involves filtering it, to remove oil and particulates, and drying it to remove moisture.
A typical example of a filter apparatus includes a filter head, which contains an inlet and an outlet, and a bowl, which threadingly engages the head to form a sealed vessel, within which a filter member is contained. The filter member is typically a tube sealed at one end, is attached to the filter head and sits within the filter bowl. A pair of conduits formed in the filter head direct air to and from the filter member. A first conduit directs the air from the inlet into the centre of the filter, the air flows through the tubular wall of the filter, up the sides of the filter bowl and then through a second conduit, which surrounds the first conduit, directing the air to the outlet. In this example the air is flowing from the inside of the filter to the outside but this flow can be reversed so that the air flows from the outside of the filter to the inside.
Maintenance of such devices includes the changing of the filter. This is done by unscrewing the bowl from engagement with the head so as to expose the filter which can then be disengaged from the filter head and replaced. However, in confined spaces the removal of the filter bowl can be extremely awkward and sufficient space must be left around the filter apparatus to allow the maintenance to take place. This additional space present significant design limitations to the use of this type of filter in certain situations. Furthermore, when a filter is being replaced it is often coated around its outside with a layer of oil making the used filter difficult and messy to handle.